Centrifugal fan with resonant silencer

ABSTRACT

A centrifugal fan with a resonant silencer has a centrifugal impeller and an outer housing. The outer housing has an inlet, an outlet and a resonant silencer. An inlet is positioned along an axial direction of the centrifugal impeller. An outlet is positioned along a radial direction of the centrifugal impeller. The resonant silencer, extended from a cut-off, can reduce noise caused by a vortex. The resonant silencer can be I- or L-shaped. The cut-off can be covered by a net filter, which isolates the resonant silencer from the flow motivated by the centrifugal impeller.

RELATED APPLICATIONS

The present application is based on, and claims priority from, Taiwan Application Serial Number 93116571, filed Jun. 9, 2004, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Field of Invention

The present invention relates to a centrifugal fan with noise reductionality. More particularly, the present invention relates to a centrifugal fan with a resonant silencer.

2. Description of Related Art

As a notebook PC becomes thinner, there isn't enough space for heat convection and heat dissipation design inside the case housing of the notebook PC. When it comes to high-frequency components, such as the CPU (central processing unit) and graphics processing chip, the heat dissipation design hits a bottleneck. Thus, the mainstream framework of heat dissipation design is forced heat convection caused by a centrifugal fan.

FIG. 1 illustrates a perspective view of a conventional centrifugal fan. A centrifugal fan includes a spiral-shaped flow channel design. A centrifugal impeller 16 transforms air dynamic energy into static pressure so as to overcome high flow impedance inside the case housing of the notebook PC. On the other hand, air 18 driven by the centrifugal impeller 16 flows through the spiral-shaped flow channel and generates a wake flow and a vortex 15, which create high-frequency and narrow-band noise.

Once heat dissipation efficiency is enhanced, airflow is essentially accelerated. The stronger the airflow is, the more turbulent the wake flow is. Thus, a notebook PC manufacturer faces a dilemma between noise reduction and heat dissipation efficiency.

SUMMARY

It is therefore an objective of the present invention to provide a centrifugal fan with a resonant silencer so as to reduce noise.

In accordance with the foregoing and other objectives of the present invention, a centrifugal fan with a resonant silencer includes a centrifugal impeller and an outer housing. The outer housing includes an inlet, an outlet and a resonant silencer. An inlet is positioned along an axial direction of the centrifugal impeller. An outlet is positioned along a radial direction of the centrifugal impeller. The resonant silencer, extended from a cut-off, can reduce noises caused by a vortex. The resonant silencer can be designed in an “I” or “L” shape. The cut-off can be covered by a net filter, which isolates the resonant silencer form the flow motivated by the centrifugal impeller.

According to the preferred embodiments, the noises, which are basically composed of blade passing frequency, are reduced when the length of the resonant silencer is equal to one-fourth the wavelength of the blade passing frequency of the centrifugal impeller. The blade passing frequency is proportional to the product of the number of blades and the blade rotation rate.

Thus, a resonant silencer of the centrifugal fan can be extended from a cut-off around an outer housing so as to reduce noises. The cut-off can be covered by a net filter for isolating the resonant silencer and preventing the same from affecting the flow channel. The resonant silencer can be made of an elastic material (such as a plastic tube) so as not to occupy much space.

It is to be understood that both the foregoing general description and the following detailed description are examples, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,

FIG. 1 illustrates a perspective view of a conventional centrifugal fan;

FIG. 2A illustrates a perspective view of a centrifugal fan with an I-shaped resonant silencer according to one preferred embodiment of this invention;

FIG. 2B illustrates a graph of how an I-shaped resonant silencer reduces noises according to one preferred embodiment of this invention;

FIG. 3 illustrates a perspective view of a centrifugal fan with an L-shaped resonant silencer according to another preferred embodiment of this invention; and

FIG. 4 illustrates a perspective view of an outer housing of a centrifugal fan according to one preferred embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

In order to obviate the need to choose between noise and heat dissipation efficiency, the present invention discloses a centrifugal fan with a resonant silencer. According to experiment results, a basic noise source lies in the friction between a wake flow and a cut-off of a spiral-shaped outer housing of a centrifugal fan. Thus, a resonant silencer is designed to eliminate noise near the cut-off.

FIG. 2A illustrates a perspective view of a centrifugal fan with an I-shaped resonant silencer according to one preferred embodiment of this invention. A centrifugal fan with a spiral-shaped flow channel 25 is illustrated. When a centrifugal impeller 26 rotates counter clockwise, the basic noise source lies in a cut-off region 22 due to the friction between the cut-off 22 and a wake flow passing by. In this embodiment, a resonant silencer 20 extends from the cut-off 22 of the outer housing 24. A length D of the resonant silencer 20 is determined relative to a blade passing frequency of the centrifugal impeller 26; i.e., the length D is equal to one-fourth the wavelength of the blade passing frequency of the centrifugal impeller 26. The blade passing frequency is proportional to the product of the number of blades and the blade rotation rate.

FIG. 2B provides a graph of how an I-shaped resonant silencer reduces noise according to one preferred embodiment of this invention. Incident waves 28A and reflective waves 28B thereof both appear in a resonant silencer 20. When a length of the resonant silencer 20 is one-fourth the wavelength of a blade passing frequency of the centrifugal impeller 26, incident waves 28A and reflective waves 28B thereof interfere with each other, resulting in noise reduction. The resonant silencer 20 is isolated from the flow channel 25 by a net filter 30 (referring to FIG. 4) so as not to influence flow field and pressure distribution. The resonant silencer 20 can be made of an elastic material (such as a plastic tube) to accommodate space restriction in a notebook computer. A resonant frequency and a performance of the resonant silencer 20 vary as a function of the resonant silencer 20 volume, via hole cross sectional area of the net filter 30, via hole number of the net filter 30 and a thickness of the net filter.

FIG. 3 illustrates a perspective view of a centrifugal fan with an L-shaped resonant silencer according to another preferred embodiment of this invention. A centrifugal fan with a spiral-shaped flow channel 25 is illustrated. When a centrifugal impeller 26 rotates counterclockwise, the basic noise source lies in a cut-off 22 due to friction between the cut-off 22 and a wake flow passing by. In this embodiment, a resonant silencer 20 extends from the cut-off 22 around the outer housing 24; thus, the resonant silencer 20 is L-shaped.

The above embodiment is used to reduce noise, composed of low, medium frequency sound, whose frequency is equal to a resonant frequency of the resonant silencer 20 so that widespread haystack-waveform noises are formed to make a listener feel more comfortable. The resonant frequency and a performance of the resonant silencer 20 vary as a function of the resonant silencer 20 volume, via hole cross sectional area of the net filter 30, via hole number of the net filter 30 and a thickness of the net filter. An optimum design of the resonant silencer 20 and the net filter 30 can create a balance point between noise and flow rate.

FIG. 4 illustrates a perspective view of an outer housing of a centrifugal fan according to one preferred embodiment of this invention. An outer housing 24 includes an inlet 29 and an outlet 27. The inlet 29 is positioned along an axial direction of the centrifugal impeller 26; the outlet 27 is positioned along a radial direction of the centrifugal impeller 26. The enlarged view of a cut-off region 22 is illustrated on the right side of FIG. 4 and the cut-off region 22 is covered by a net filter 30.

According to the preferred embodiments, a resonant silencer of the centrifugal fan can be extended from a cut-off around an outer housing so as to reduce noise. The cut-off can be covered by a net filter for isolating the resonant silencer and preventing the same from affecting the flow channel. The resonant silencer can be made of an elastic material (such as a plastic tube) so as not to occupy much space.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents. 

1. A centrifugal fan with a noise reduction functionality, said centrifugal fan comprising: a centrifugal impeller; and an outer housing, said centrifugal impeller being housed inside said outer housing, said outer housing comprising: an inlet, positioned along an axial direction of said centrifugal impeller; an outlet, positioned along a radial direction of said centrifugal impeller; and a resonant silencer, extending for a predetermined distance from a cut-off of said outer housing, wherein said predetermined distance is proportional to a wavelength of a blade passing frequency of said centrifugal impeller.
 2. The centrifugal fan of claim 1, wherein said predetermined distance is one-fourth the wavelength of said blade passing frequency of said centrifugal impeller.
 3. The centrifugal fan of claim 1, wherein said resonant silencer is made of an elastic material.
 4. The centrifugal fan of claim 1, wherein said resonant silencer is made of a plastic tube.
 5. The centrifugal fan of claim 1, wherein said resonant silencer is made of an I-shaped structure.
 6. The centrifugal fan of claim 1, wherein said resonant silencer is made of an L-shaped structure.
 7. The centrifugal fan of claim 1, further comprising a spiral-shaped flow channel between said centrifugal impeller and said outer housing.
 8. The centrifugal fan of claim 1, wherein said cut-off is covered by a net filter.
 9. The centrifugal fan of claim 1, wherein said blade passing frequency is proportional to a product of a number of blades and a blade rotation rate.
 10. A centrifugal fan with a noise reduction functionality, said centrifugal fan comprising: a centrifugal impeller; and an outer housing, said centrifugal impeller being housed inside said outer housing, said outer housing comprising: an inlet, positioned along an axial direction of said centrifugal impeller; an outlet, positioned along a radial direction of said centrifugal impeller; a cut-off, positioned near said an outlet; and a resonant silencer, extending from said cut-off around said outer housing, said resonant silencer having a resonant frequency, wherein said cut-off is covered by a net filter.
 11. The centrifugal fan of claim 10 further comprising a spiral-shaped flow channel between said centrifugal impeller and said outer housing.
 12. The centrifugal fan of claim 10, wherein said resonant silencer is made of a plastic tube.
 13. The centrifugal fan of claim 10, wherein said resonant silencer is made of an I-shaped structure.
 14. The centrifugal fan of claim 10, wherein said resonant silencer is made of an L-shaped structure.
 15. The centrifugal fan of claim 10, wherein said resonant frequency and a performance of said resonant silencer vary as a function of said resonant silencer volume, via hole cross sectional area of said net filter, and via hole number of said net filter and a thickness of said net filter.
 16. A centrifugal fan with a noise reduction functionality, said centrifugal fan comprising: a centrifugal impeller; and an outer housing, said centrifugal impeller being housed inside said outer housing, wherein said outer housing includes a resonant silencer, extending for a predetermined distance from a cut-off of said outer housing, said resonant silencer having a resonant frequency for reducing noise.
 17. The centrifugal fan of claim 16, wherein said predetermined distance is proportional to a wavelength of a blade passing frequency of said centrifugal impeller.
 18. The centrifugal fan of claim 16, wherein said resonant silencer is made of an I-shaped structure.
 19. The centrifugal fan of claim 16, wherein said resonant silencer is made of an L-shaped structure.
 20. The centrifugal fan of claim 16, wherein said cut-off is covered by a net filter. 